This video by Animalist finally has the answer as to why most dogs hate mailmen and delivery people and there’s a solid reason why they do. It is all about trespassing!
In a dog’s perspective, mailmen are people trespassing their property. When they see a stranger coming, dogs will do everything to protect their territory. They start to display aggressive signs in an attempt to scare off the intruder. The mailman – who is just doing his job – comes and goes in a matter of seconds. From the dog’s perspective, his threatening behavior “worked” in getting rid of the trespasser so the next time the delivery person comes, the dog remembers that his tactics worked the first time. So he does it again. This becomes a habit that will go on and on if left uncorrected.
So how to correct this behavior?
Introducing them to each other helps a lot. When the mail comes, go and greet the mailman to let your dog know that there are no dangers present. Or you can give the mail carrier your dog’s favorite treat so he can offer goodies to your worried pet. With good training, your dog will most likely look forward for the next mail to arrive.